This means you should not install the default PHP package for your distribution when the distribution also runs on Zend Server. This Facter plugin will allow you to use the $zendserver fact inside your own manifests to check if Zend server is installed, so you can take measures against installing stuff that is taken care of by ZendServer itself.

You can download the plugin from his github account, https://github.com/jaytaph/puppet-facter-zendserver, and easily install it into your puppet setup.